Pressure sensitive adhesives (PSA) are a class of adhesive compositions that are applied with slight pressure, which can be finger pressure, and generally do not undergo a liquid to solid transition in order to hold materials together. PSAs can be solvent-free natural or synthetic resins having a viscoelastic property termed tack. Tack is a property characterized by the rapid wetting of a substrate by a polymer to form an adhesive bond upon brief contact with the substrate under light pressure.
Pressure-sensitive adhesives (PSAs) form a permanent tacky film that, even under slight pressure, sticks to a very wide variety of surfaces. Pressure-sensitive adhesives are used to produce self-adhesive products such as self-adhesive labels, tapes, films, decals, decorative a vinyls, laminates, wall coverings, and floor tiles. Products of this kind are very simple to use and make it possible to work rapidly when bonding. In contrast to contact adhesive compositions, no ventilation times are necessary. Moreover, there is no “open time” within which the adhesive bond must be implemented. The quality of a self-adhesive article depends on whether the internal strength (cohesion) and the sticking of the adhesive film on the surface that is to be bonded (adhesion) are set properly in relation to one another in accordance with the utility.
In the case of pressure-sensitive adhesive labels, for example, the level of pressure-sensitive adhesive cohesion must be sufficient for no stringing and no emergence of glue at the edges to occur in the course of stamping and cutting, since otherwise the cutting tools become soiled and the cut faces sticky. At the same time, the adhesion should be sufficiently high to obtain an adequate bond to the substrate.
Generally, pressure sensitive adhesives can be designed to perform in a broad temperature range, or in a narrow temperature range. When being able to perform in a narrow temperature range, PSAs can be designed to obtain desired properties. When designed for a broad temperature range, generally some properties of the PSA will perform better at a given range within the broad range rather than similarly over the broad range.
In the all temperature market of pressure sensitive adhesives (generally −30° C. to 50° C.), PSAs can achieve adequate adhesion or they can achieve adequate cohesion. In general it is not possible to optimize adhesion and cohesion independently of one another. Trying to optimize one generally reduces the other. It would be desirable to obtain an All-Temperature pressure sensitive adhesive that provides adhesion and tack for a broad temperature range while maintaining cohesion at a high level.